Therapeutically cloned stem cells work in mice

If the use of stem cells wasn't controversial enough on its own, it quickly became entangled in another ethical issue: the potential for human cloning. A technique, termed therapeutic cloning, involves creating embryonic stem cells that are genetically identical to an adult disease victim; those stem cells could then be used to repair damaged tissue. The technique itself, however, could possibly be adapted to create a viable cloned embryo, which has made some bioethicists and the public a bit nervous.

A simple question has been lost in the controversy: would it actually work? It was entirely possible that the ethical debates were raging about a technique that would ultimately fail to live up to its promise. Yesterday, Nature Medicine released a paper that describes how, in mice, therapeutic cloning works exactly as promised. I know two of the authors of the paper, and briefly collaborated with them on related work, but was not involved in this project.

The new research focused on the treatment of Parkinson's disease, which is caused by the loss of dopamine-producing neurons in a specific region of the brain, and results in loss of muscle control. In mice, parkinsonian symptoms can be induced by injecting the brain with a chemical related to dopamine that kills the cells that normally produce it. The authors of the new study performed this procedure on mice, then sent tissue from the mouse's tail to a group in Japan that are experienced in the production of embryonic stem cells through the use of somatic cell nuclear transplant. The resulting stem cells were shipped back to New York City, where they were used to produce neural stem cells and, ultimately, midbrain dopamine neurons.

These were injected into the brains of the mice that had originally donated the genetically matched tail tissue. By five weeks after transplantation, the mice's parkinsonian symptoms were dramatically improved. When the mice were sacrificed, an examination of their brains revealed many new dopamine producing cells derived from the cloned stem cells. When the same cells were injected into an unrelated mouse, symptoms were not improved, and later analysis revealed that none of the stem cells survived; tests suggested that they had been killed by an immune response.

Not all of the experiments went flawlessly. A few of the stem cell lines developed chromosomal abnormalities, and a few of the grafts were contaminated with immature cells that grew out of control. It should also be noted that the experimental treatment may produce Parkinson's symptoms, but may not accurately reproduce the disease state, so these experiments should not be viewed as demonstrating a method of curing Parkinson's.

The experiments do, however, clearly demonstrate that therapeutic cloning lives up to its promise in terms of providing stem cells that are genetically matched to the donor. This allows them to integrate with their donor's tissue and avoid attack by its immune system. Other recent papers have described the production of embryonic stem cells without the use of somatic cell nuclear transplant, which may ultimately allow similar transplants to be performed using cells that are associated with fewer ethical concerns.